The thermal conductivity of bulk GaN grown by Hydride Phase Vapor Epitaxy with intentional Si doping was measured using the 3 method. The effect of Si concentration ranging from 1.6x10(16) to 7x10(18)cm(-3) on the thermal conductivity was studied over the temperature range of 295-470K. The room temperature thermal conductivity was found to decrease with increasing Si doping from 245 to 210W/m.K. Also, for each Si doped sample the thermal conductivity decreases with increasing temperature. The experimental data were analysed by a modified Callaway model and the contribution of different resistive phonon scattering process was examined. It was found that in n-type GaN the phonon-free-electron scattering became an important resistive process that leads to a reduction of the thermal conductivity at high temperatures. At the highest free electron concentrations, electronic thermal conduction was found to play a role in addition to lattice thermal conduction and compete with the effects of phonon-free-electron scattering. (C) 2017 WILEY-VCH Verlag GmbH amp; Co. KGaA, Weinheim